Re: [PATCH 06/10] commit-graph.c: sort index into commits list

On 8/3/2020 2:57 PM, Taylor Blau wrote:

For locality, 'compute_bloom_filters()' sorts the commits for which it
wants to compute Bloom filters in a preferred order (cf., 3d11275505
(commit-graph: examine commits by generation number, 2020-03-30) for
details).

The subsequent patch will want to recover the new graph position of each
commit. Since the 'packed_commit_list' already stores a double-pointer,
avoid a 'COPY_ARRAY' and instead keep track of an index into the
original list. (Use an integer index instead of a memory address, since
this involves a needlessly confusing triple-pointer).

It took me a little while to grok that we are switching from sorting
a list of commit pointers to sorting a list of integers. However, that
makes a lot of sense. It preserves the commit list sorted by OID for
binary search, which you will need soon. Perhaps another change would
need that at another time, too.

Alter the two sorting routines 'commit_pos_cmp' and 'commit_gen_cmp' to
take into account the packed_commit_list they are sorting with respect
to. Since 'compute_bloom_filters()' is the only caller for each of those
comparison functions, no other call-sites need updating.

Parsing the changes to these functions is the most complicated, because
of the int-to-commit indirection. I think they are correct and as easy
to read as possible.

-Stolee